ICE type checking incorrect impl decl

[brson]

enum chan { }

iface channel<T> {
    fn send(v: T);
}

// `chan` is not an iface, it's an enum
impl of chan for int {
    fn send(v: int) { fail }
}

fn main() {
}

rust: upcall fail 'non-exhaustive match failure', /home/banderson/Dev/rust3/src/rustc/middle/typeck.rs:1507
error: internal compiler error: unexpected failure
note: the compiler hit an unexpected failure path. this is a bug
note: try running with RUST_LOG=rustc=0,::rt::backtrace to get further details and report the results to github.com/mozilla/rust/issues
rust: upcall fail 'explicit failure', /home/banderson/Dev/rust3/src/rustc/driver/rustc.rs:232
rust: domain main @0x2615f10 root task failed
rust: upcall fail 'killed', /home/banderson/Dev/rust3/src/libcore/task.rs:454

[catamorphism]

I think this may have been accidentally fixed by code I recently committed. I'll take a look.